Identifying the position of a radiation source is required in a region that may be contaminated with radioactive substances. However, radiation is invisible to the naked eye, and cannot be directly detected even by the use of a visible-light imaging device.
One method of identifying the position of a radiation source and the traveling direction of radiation includes detecting the energy of scattered gamma rays in a Compton scattering caused by gamma rays from the radiation source and the energy of recoil electrons, and finding the traveling direction of incoming gamma rays from the energies.
Accurate detection of the Compton scattering, the energy of gamma rays, and the energy of recoil electrons tends to increase the size and complexity of a detector.